calcium phosphate stone

Introduction

75-85% of all renal stones contain calcium.

Etiology

• hypercalciuria
  • renal tubular acidosis (RTA) type 1 (calcium phosphate)
    • topiramate
• reduced inhibitor excretion
  • Mg+2
  • pyrophosphates
  • citrate (RTA-1)4) primary hyperparathyroidism
• primary hyperparathyroidism
• sarcoidosis

Epidemiology

• most common in 3rd to 5th decade of life

Pathology

• 1,25-dihydroxyvitamin D3 levels may be increased
• inappropriate calciuria may occur with calcium-restricted diets
• calcium phosphate stones form in alkaline urine
• urinary citrate diminishes with increased urinary pH
  • carbonic anhydrase inhibitors (topiramate) increase bicarbonate excreted into the urine & thus urinary pH

Laboratory

• serum PTH
• renal function tests
• urinalysis & culture
  • urine microscopy
    • calcium phosphate crystals in urine
• 24 hour urine:
  • hypercalciuria: > 300 mg (men) or 250 mg (women) or > 4 mg/kg in 24 hours
  • creatinine
  • uric acid
• 24 hour urine volume
• serum Ca+2 is generally normal
• stone analysis

Management

• correcting dietary stresses
  • Na+ increases urinary Ca+2
    • diet of < 3 g of salt/day
  • animal protein increases urinary Ca+2
    • diet of < 8 oz of meat/day
• increasing urine volume > 2.5L/day
• thiazide diuretics for hypercalciuria
  • Na+ must be restricted for urine Ca+2 to decrease by 50%
  • development of hypercalcemia suggests latent hyperparathyroidism
  • amiloride may also be of benefit
• patients with primary hyperparathyroidism & urolithiasis
  • removal of parathyroid adenoma
• replacement of inhibitor substances
  • potassium citrate
  • pyrophosphate
  • magnesium oxide

More general terms

• calcium stone

Additional terms

• calcium phosphate crystals in urine